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Re: Changing TERM TERM to HUP TERM
From: |
Ole Tange |
Subject: |
Re: Changing TERM TERM to HUP TERM |
Date: |
Sun, 17 Mar 2019 23:38:43 +0100 |
On Mon, Mar 11, 2019 at 6:48 AM Gary Johnson <garyjohn@spocom.com> wrote:
>
> On 2019-03-10, Ole Tange wrote:
> > To stop GNU Parallel today you need to send TERM to make it stop
> > starting new jobs followed by another TERM to kill the running jobs.
:
> > What is your opinion?
>
> A change seems OK, but using HUP for this purpose doesn't seem like
> a good idea. Its meaning is specified in the signal(7) man page and
> that doesn't seem to match your proposed usage. How about using
> USR1 or USR2 instead?
USR1 and USR2 are already used:
LIST RUNNING JOBS
If you want a list of the jobs currently running you can run:
killall -USR1 parallel
GNU parallel will then print the currently running jobs on
stderr (standard error).
By sending GNU parallel SIGUSR2 you can toggle turning
on/off --progress on a running GNU parallel process.
If I look at the list of signals:
Signal Value Action Comment
──────────────────────────────────────────────────────────────────────
SIGHUP 1 Term Hangup detected on controlling terminal
or death of controlling process
SIGINT 2 Term Interrupt from keyboard
SIGQUIT 3 Core Quit from keyboard
SIGILL 4 Core Illegal Instruction
SIGABRT 6 Core Abort signal from abort(3)
SIGFPE 8 Core Floating-point exception
SIGKILL 9 Term Kill signal
SIGSEGV 11 Core Invalid memory reference
SIGPIPE 13 Term Broken pipe: write to pipe with no
readers; see pipe(7)
SIGALRM 14 Term Timer signal from alarm(2)
SIGTERM 15 Term Termination signal
SIGUSR1 30,10,16 Term User-defined signal 1
SIGUSR2 31,12,17 Term User-defined signal 2
SIGCHLD 20,17,18 Ign Child stopped or terminated
SIGCONT 19,18,25 Cont Continue if stopped
SIGSTOP 17,19,23 Stop Stop process
SIGTSTP 18,20,24 Stop Stop typed at terminal
SIGTTIN 21,21,26 Stop Terminal input for background process
SIGTTOU 22,22,27 Stop Terminal output for background process
The signals SIGKILL and SIGSTOP cannot be caught, blocked, or ignored.
Next the signals not in the POSIX.1-1990 standard but described in
SUSv2 and POSIX.1-2001.
Signal Value Action Comment
────────────────────────────────────────────────────────────────────
SIGBUS 10,7,10 Core Bus error (bad memory access)
SIGPOLL Term Pollable event (Sys V).
Synonym for SIGIO
SIGPROF 27,27,29 Term Profiling timer expired
SIGSYS 12,31,12 Core Bad system call (SVr4);
see also seccomp(2)
SIGTRAP 5 Core Trace/breakpoint trap
SIGURG 16,23,21 Ign Urgent condition on socket (4.2BSD)
SIGVTALRM 26,26,28 Term Virtual alarm clock (4.2BSD)
SIGXCPU 24,24,30 Core CPU time limit exceeded (4.2BSD);
see setrlimit(2)
SIGXFSZ 25,25,31 Core File size limit exceeded (4.2BSD);
see setrlimit(2)
I find it pretty clear that I cannot use a signal whose action is
'core': Those are not even close in meaning.
Neither are the ones with the action 'stop'. SIGURG is also not close
in meaning. SIGCHLD is used actively, so that rules that out.
So we are in reality down to the ones with action 'term'. And asking
GNU Parallel not to start more jobs is kind of asking it to terminate
soonish.
SIGALRM has a wrong ring to me.
SIGPIPE will no doubt be triggered by other means.
SIGINT is ctrl-C and should stay the same.
SIGKILL will kill GNU Parallel here and now - no cleanup. And it
cannot be caught.
SIGTERM will make GNU Parallel kill children and clean up.
That leaves SIGHUP.
I know SIGHUP is used in some daemons to say 're-read your config',
which is also not really the situation described in 'man 7 signal'.
I have now committed a version where SIGHUP is used. Can I ask you to
try to make it fail/do odd things that version 20190222 does not do?
If I do not hear any reports before Thursday, I will leave it in and
make it clear in next release that this is experimental (so that if we
discover bad behaviour, it will be rolled back).
/Ole